What is biogas ? Biogas typically refers to a gas produced by the biological breakdown of organic matter in the absence of oxygen . One type of biogas is produced by anaerobic (without air) digestion or fermentation of biodegradable materials such as biomass manure or sewage ,municipal waste and energy crops.

Background?

According to a Herald report sometime in February , 2008 the Zimbabwe National Water Authority (ZINWA) indicated that they were considering reviving the biogas digesters that have been lying idle at Firle and Crowborough waterworks in Harare to cut down on energy costs.

Studies done at Crowborough site in Kuwadzana revealed that the gas produced has a chemical composition of 66,4 percent methane, 32,2 percent carbon dioxide and the rest hydrogen sulphide.?

If revived, the digesters also have the capacity of producing enough energy to drive several other industrial operations that require large amounts of power. According to water experts Crowborough wastewater in Kuwadzana, currently consumes almost 215 000 kilowatts each month, costing the water authority billions of dollars yet it has the potential of producing about 12 500-cubic metres of biogas a day.

Example

An interesting success story on biogas technology deployment in Africa is in Rwanda. This followed the exponential rise in prisoner population following the genocides around mid 90s. With some of Rwanda?s prisons holding five times the intended number of inmates, it?s not surprising that the original septic tanks and settling pools were unable to cope. The appearance and stench was just the beginning of the problem. Faced with these threats, the Kigali Institute of Science & Technology KIST developed a way to convert the human sewage to biogas, thus cleaning up the waste hygienically and creating a sustainable energy source? - that?s killing 2 birds with one stone.

Technology

Biomass technology is a very mature and old technology that formalizes the decomposition of waste into a fuel (biogas) and some fertilizer (waste).This process is part of the natural carbon cycle of life. The sunlight produces food in plants that we eat and discard as waste. As you know, you can neither create nor destroy energy but convert it to one form or another.

Methane (CH4) is the combustible component of biogas. On average biogas has like 60 % methane.

Developing countries like Vietnam , Brazil , Thailand , Phillipines and of late Tanzania and Rwanda have matured and stabilized in this technology.

The process

A quick summary of the actual digestion process or decomposition (kuwoora - ukubola) .

Anaerobic digestion is one of the most common biological procedures in nature, as the name implies, it means to carry out digestion or breakdown in the absence of air. Anaerobic decomposition will produce methane, carbon dioxide, some hydrogen and other gases in traces, very little heat. Biogas technology simply formalizes the natural decomposition process.

Anaerobic decomposition is a two-stage process as specific bacteria feed on certain organic materials at a specific pH level. In the process, the bacteria emit gases, mostly methane. But instead of being vented into the air, they are piped into a storage canister.

Depending on temperature and moisture content, it takes about 6?25 days to fully process a batch temperatures are pretty favorable for this process in most parts of Zimbabwe. The end product is about 60?70% methane and 20?30% CO2, with small amounts of hydrogen sulfide and other impurities.

Challenges

Constraints of biogas production arise from the production rate limitations. The process of anaerobic decomposition is relatively slow, so production of gas at useful rates required large volume of permanent culture. Biogas is not easily bottled and thus must be used near its sources. Thus biogas can not be produced on an as needed basis or where needed basis. Thus it makes economic sense for public municipalities like Harare, Bulawayo, Gweru, Mutare etc to be the initiators of such projects since they own and or operate water/waste management systems.

Beyond concerns about sanitation, successful adoption of biogas in the developing world is highly dependent on political, economic, logistical, and social factors. It is important that decision makers understand what this biomass technology is if it?s to be rolled out effectively. Like any other technology adoption is usually problematic.

Way forward

A healthy prospect for Zimbabwe is the development of a anaerobic wastewater treatment systems with biomass as a by product . There is no shortage of raw materials to be used as stock feed as we are aware that some urban centers in Zimbabwe are literally flowing with raw sewage. Biomass technologies will not totally eradicate power shortages in Zimbabwe , but will go a long way in alleviating? ZESA of the burden if executed properly.

Municipalities, hospitals, prisons, colleges , schools etc should seriously consider adopting this technology which is already being used in various parts of the world. It?s not a question of its suitability and cost effectiveness, but a question of whether the decision makers have enough vision to comprehend the advantages biomass technologies.

It takes 1?2 cows, 5?8 pigs, or 4 adult humans to supply adequate daily feedstock for a single-household biodigester, according to a UNDP?Global Environment Facility fact sheet. Hence the use of biodigesters makes sense for institutions like prisons and hospitals and colleges where human population density is higher than elsewhere.

The cost per unit of energy over a digester?s 15- to 20-year life cycle is lower than both solar electrification and the cost of extending a conventional electrical grid. For farmers this is particularly very crucial to the farmers who need energy and or electricity to process their produce or to cure their tobacco !

The departments responsible for energy must think outside the box in a new Zimbabwe and tap into this very old and very stable technology. There are some biomass plants somewhere in Chishawasha that were installed as far back as 1979.

Organizations like the Netherlands Development Organization (SNV) Asia-Africa on Renewable Energy/Biogas Programme have been rolling out biomass plants to Tanzania for years now. There is no shortage of technology of funding on part of the donors .But what remains elusive is the commitment, focus and accountability on part of developing countries.

Cost and ROI

Biomass digesters which range anything from $ 400 to $ 1500 depending on type and capacity. The digester can be plastic containers or made out of brick and cement constructions.?

There are many designs of biogas plants which are available but the most common are the floating canopy (Indian) and fixed dome (Chinese) models. The polyethylene tubular biodigester technology is a cheap and simple way to produce gas for small-scale farmers. It is appealing to rural people because of the low cost of the installation and therefore of the gas, and the improvement in the environment that the installation allows. It can be applied in rural or urban areas, both in low and hilly lands.?

Conclusion

We need to confront the problems that face us at the same level at which they occur. Naturally , pessimists and critics alike , might think that these efforts are far fetched since the economy is really challenged. Yes the economy is on its knees because we are always looking for help elsewhere.?

If we fail to turn around the economy we have no-one else to blame other than ourselves. Of course such efforts will only have a realistic ?take off? opportunity when a political solution is finally arrived at. But we don?t stop planning because there is a political impasse. The clock never stops turning just because one is facing challenges and problems !

Human waste may be a stinky business, but to some , it smells like money !

Lets hear you thoughts on the revitalizing those plants that are already in existence and also the adoption of biomass technologies.

Robert Ndlovu ,
New York , USA .
robertndlovu@yahoo.com